For over a year, Michael van den Heuvel researched square coins issued throughout the world between 1900 and 2000. The result is this limited-run reference book, with information about all 26 countries and territories which minted square coins during that time. Each coin includes pictures of the obverse and reverse, the years it was minted, its composition, mintmarks, and mintage (number of coins made per year) where possible. Also included with many coins is information about the country, coin, and/or the designer/engraver. I don't think you'll find a similar reference for world square coins anywhere.